The present invention relates to a video signal encoder, especially a digital video signal encoder which encodes computer graphics.
The book "Video Demystified," Second Edition, by Keith Jack, incorporated herein by reference, describes the background for digital video encoding and decoding. On computers, color information pixels are typically stored in the red/green/blue (RGB) color space. For video encoding, the RGB data is converted into data including an intensity signal, and two chrominance signals. The intensity information is the equivalent of the black and white image of a television signal. In the YUV color space, "Y" stands for the intensity or luminance, and "U" and "V" contain the chrominance or color information. Another way of representing pixel data is in the Hue-Saturation-Intensity (HSI) color space. In this color space, the intensity corresponds to the black and white image; the hue, which is typically represented as a phase, indicates a color, such as red or blue; and the saturation indicates the level of the color, such as a pink versus a dark red. The most common television standards are the National Television Standards Committee (NTSC) standard used in the United States and the Phase Alternation Line (PAL) standard used in many European countries. In both of these standards, the chrominance information is encoded on a chrominance subcarrier. The hue is encoded as the phase of the chrominance subcarrier compared to the burst signal. The saturation is encoded as the amplitude of the chrominance subcarrier.
A problem that has been noted in the past is that of color distortion between two adjacent colors when phase (hue) and saturation encoding is used based on the HSI color space. This color distortion is caused by the change in the chrominance signal between the pixels. It is desired to provide an improved system which can reduce some of the color distortion between the video pixels.